Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 172300

Area Forecast Discussion
National Weather Service Sacramento CA
300 PM PST Wed Jan 17 2018

Active weather pattern continues, with a cold storm system arriving
Thursday-Friday. A similarly cold and wet storm system is expected



Main forecast concerns for the short term period are the incoming
winter storm tonight through Friday that will bring heavy
accumulating snow for the mountains and snow levels to around 2500
to 3000 feet and widespread rainfall across the valley.

Latest satellite imagery and model upper level analysis shows the
incoming upper level low positioned just off the Washington
coastline with height falls across northern California. Plenty of
moisture ahead of the disturbance is leading to increased cloud
cover across the forecast area as well as a moist environment,
leading to a slow fog dissipation from the morning hours. Patchy
fog will possibly continue through the evening hours until rain
begins sometime late this evening through the overnight hours.

The main impactful weather from the storm will result in
precipitation up to an inch for the valley and between 1 and 2
feet of snow for the Sierra through Friday. Travel for the I-80
and US 50 corridors could become difficult or even impassible
without chains. Gusty winds between 25 and 35 mph could make
travel difficult for higher profile vehicles.

Trough base swings through sometime Friday afternoon through
Friday night, which will end the main accumulation period of
precipitation across the area. A shortwave ridge of high pressure
will develop Saturday with the potential for clearing skies and
patchy fog for the valley before the next weather making system
arrives Saturday night into Sunday.



Another weather system is expected to impact NorCal Sunday through
Monday. Precipitation will initially impact the Coastal Range
early Sunday before slowly spreading southeast throughout the day.
This storm is expected to be cooler with snow levels 3000 to 5000
feet. Precipitation amounts keep fluctuating between model runs
for this storm, though they all seem pretty confident that this
will be a slightly wetter storm for the valley and areas north of
Interstate 80 than the more recent storm. The valley can expect
half an inch to an inch of rain with locally up to 2 inches over
the Northern Sierra. The Coastal Range is expected to receive the
most precipitation of the season so far with liquid precipitation
values of 2 to 3 inches possible. Snow amounts could reach up to a
foot over the higher elevations of the Coastal Range.

Light precipitation could linger over the higher elevations
Tuesday. Models continue to show a continuation of the wet pattern
with another storm system moving in mid to late week. Details are
still pretty hazy this far out, so keep an eye on the forecast for
updates. HEC



MVFR/IFR conditions, local IFR, due to low ceilings will continue
through the evening. Another round of valley fog could be
possible after 06z Thursday from KSMF southward. Rain will impact
the northern Sacramento valley after 3z Thursday, moving southward
after 12z. Winds remain under 15 knots. HEC


Winter Storm Warning from noon Thursday to 4 PM PST Friday for
West Slope Northern Sierra Nevada-Western Plumas County/Lassen

Winter Weather Advisory from 7 PM Thursday to 4 PM PST Friday
for Mountains Southwestern Shasta County to Northern Lake County-
Shasta Lake Area / Northern Shasta County.


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